Hallå alla Svenskar! Nåja, vi tar det på Engelska.

Hello! I have a problem with the three Swedish letters: ÅÄÖ, on my forum.
When I write a post, they work. But when OTHERS do it, the letters transforms to strange things like: ?

Please, can somebody help me? Fast!
Im not so god at PHP and so on, but if someone describes exactly how to do, i'll know how to fix it!

//Milan (http://bussmilan.se/bussforum/)

(I use the English langpack at the moment, but should i download the Swedish?)